The present invention relates to a dimmer unit for wall mounting having a construction suitable for large volume manufacture but having a power handling capacity of a level higher than dimmer units conventionally manufactured in high volume.
It is known that dimmer units are employed in homes and other buildings for controlling the level of lighting within such buildings by providing a solid state switching action. Such solid state switching action can occur during each half cycle of the normal 60 cycle voltage alternation of the current supply. This switching permits a portion only of the power which could otherwise flow during each half cycle to be in fact transmitted to the lighting device. Such switching is accomplished by a solid state device incorporated within a phase control switching circuit of the dimmer unit.
The circuit which controls the solid state switching is enclosed within an insulating housing and the housing is of a size to permit mounting within a single standard wall box. A dimmer unit may be mounted initially by an electrician in a conventional wall box or an electrician may replace an ON-OFF switch which has been previously mounted in such a wall box. It is important in the use of dimmer devices in such wall box applications that they not occupy more total enclosed volume in the wall box than is available therein and which is conventionally occupied by a standard ON-OFF switch together with the wire leads and connectors of the switch.
One reason for the widespread use of dimmer units is that it has been found technically feasible to build dimmers in such fashion that it is possible to use them to replace conventional ON-OFF switches in conventional wall boxes. To make such replacement economically practical, there has been developed as an economical article of commerce a dimmer switch unit having a metal mounting strap and having an insulating housing from which two wire leads or two wire screw terminals extend. In the conventional dimmer unit the solid state compartment, which may normally be a triac or quadrac, is in thermal communication with the metal mounting strap but is electrically isolated from this metal mounting strap.
It has been found to be quite important in the substitution by the average homeowner of dimmer units for standard ON-OFF switching units, that the overall dimmer device fit conveniently and easily within the conventional wall box enclosure from which the ON-OFF switch has been removed. One reason for this is that a replacement is the simplest arrangement by which a homeowner may convert an ON-OFF lighting circuit to a dimmer circuit. The homeowner simply removes the switch plate, and then removes the ON-OFF switch by demounting it from the wall box. Next he disconnects the two electric supply wires connected to the switch. He then connects the same two electric supply wires to a dimmer switch unit, and mounts the dimmer unit in the wall box in place of the switch. All that remains to be done is to replace the same switch plate and press the dimmer control knob into place.
One of the advantages of such economical solid state dimmer units which can be fitted within the conventional wall box is that millions of average homeowners can convert their lighting controls to dimmer controls as simply as they can replace a wall switch. Often this is done by an electrician but more often it is done by the homeowner because of the inherent simplicity of the change. There is no resulting difference from the replacement by a dimmer unit other than the presence of the conventional dimmer control knob used in regulating the lighting level through the dimmer unit.
Consequently a very substantial number of dimmer units having the capability of controlling about 600 watts are installed each year. These units are of conventional construction, fit in the conventional wall box, and may be covered by the conventional wall plate without detracting from the appearance of the control article at the switch location. Several millions of such 600 watt devices are installed each year by homeowners and this has been the case for a number of years.
In many applications, it is desirable to employ dimmers of higher wattage rating but the cost of such dimmers is sufficiently high so that there is a tendency for a person who wishes to use, for example 1000 watts of control to purchase two of the lower rated 600 watt dimmers and to use these in adjoining wall boxes as the control element providing the 1000 watt load can be split into two separate loads, as dimmers cannot be operated in parallel. When a 600 watt dimmer is used in a wall box adjacent to another 600 watt dimmer, both dimmers must be derated so that the use of two side-by-side dimmers in a wall installation provides about 1000 watts of control. The use of two dimmers is most suitable for new building construction as separate wiring must extend from the installed dimmers to the lighting loads to be controlled and such separate wiring can be installed most efficiently and at lowest cost before the walls and other interior of a building are formed into place. Rewiring a building after it is finished to provide separate wires to separate loads is more costly and sometimes simply not feasible economically.
The conventional No. 14 wire used in building construction will handle 15 amperes or 1800 watts of power at the 120 voltage level commonly used. Accordingly, the wire in the control circuit used for control of 600 watts is capable of handling much higher wattage. The 600 watt dimmer is the product most commonly installed primarily because the 600 watt control capacity is sufficient to handle most light fixtures controlled by a wall switch. Further the 600 watt capacity represents the practical operating wattage level at which heat from the solid state device can be adequately dissipated from an aluminum mounting bracket within a standard wall box, although the 600 watt rating is below the switching capability of the solid state device itself. Also, the 600 watt dimmer can be installed as a full mechanical substitute of an ON-OFF switch. Once installed it is completely covered by a conventional wall switch plate as explained above and the plate may be for example the one previously used in covering the ON-OFF switch.
Because of such ready convertability of such switches to in-wall dimmers, they are produced in very large numbers. The advantages of such large volume production are made available to the purchasing public. One such advantage is the lower cost of such in-wall dimmer devices to the public because of the lower cost or manufacture which results from the higher number manufactured.
In situations in which a higher lighting load, above about 600 watts, is to be controlled by a dimmer, it is not economically feasible to alter the wiring to employ more than one 600 watt dimmer. A higher rated dimmer may be installed in a single wall box. Such higher rated dimmers conventionally have heat dissipation fins or heat sinks which are external to the wall surface. Also such higher rated dimmers are produced in smaller numbers at substantially higher cost than the more standard lower wattage in-wall dimmers.